Muffler for internal combustion engine

ABSTRACT

The subject invention refers to a muffler comprising a muffler housing ( 1, 2 ) and generally a catalytic converter element ( 13 ) mounted in the housing, which muffler has at least one inner outlet ( 4 ) through which exhaust gases cleaned by the catalytic element ( 13 ) are intended to pass. Furthermore, according to the invention an outlet duct ( 30, 31 ) is arranged in connection to the outside of the housing, comprising a first section ( 30 ) for leading exhaust gases in a first direction (A) in parallel with the outside of the housing, and a second section ( 31 ) for leading exhaust gases in a second, opposite direction (B), whereby said first and second sections ( 30, 31 ) have an essentially equally large cross-sectional area. By way of this outlet duct an improved cooling of the exhaust gases before they are brought in contact with fresh air rich in oxygen can be achieved. A back-pulsation of fresh air into the muffler can also be prevented.

This application claims the benefit of International Application NumberPCT/SE00/02158, which was published in English on May 10, 2002.

TECHNICAL FIELD

The subject invention refers to a muffler comprising a muffler housingand generally a catalytic converter element mounted in the housing, saidmuffler has at least one inner outlet through which exhaust gases areintended to pass.

BACKGROUND OF THE INVENTION

Cleaning of exhaust gases by using catalytic converters has nowadaysbecome more and more common even in smaller internal combustion enginesof two-stroke type, e.g. in handheld power-driven working tools, such aschain saws and grass trimmers. Demands concerning weight and size of theexhaust cleaning equipment have led to the development of so calledcatalytic mufflers which are mounted directly to the exhaust port of thecylinder. A typical catalytic muffler has a sealed housing with an inletas well as an outlet port, and a catalytic element mounted in thehousing for cleaning the exhaust gases leaving the muffler. Furthermoreit is often advantageous to release the exhaust gases through the lid ofthe muffler, see WO9602741.

A consequence of the introduction of catalytic conversion is that thetemperature of the exhaust gases has increased considerably owing to thereactions in the catalytic converter. The compact design of theabove-mentioned type of catalytic muffler results in that the exhaustgases will leave the muffler relatively soon after they have passedthrough the catalytic converter, and thus extremely hot exhaust gasesare released from the muffler. Furthermore it is common that the plateparts of the muffler will enclose the catalytic converter elementrelatively tight, and so called “hot spots”, i.e. surface areas of thecatalytic element getting an extremely high temperature, can spread evento surrounding plate parts. When fresh air, i.e. air rich in oxygensurrounding the engine, comes into contact with the extremely hotexhaust gases, or with these “hot spots”, flames could occur. This couldlead to an increased risk of fire, particularly since this type ofsmaller engines are often used in tools handled in fire riskenvironments with plenty of inflammable material.

In order to essentially eliminate the risk of fire caused by sparks acatalytic muffler of this kind is often equipped with a spark-arresterscreen, which even is a requirement in US-legislation. For obtaining asatisfactory result the spark-arrester screen must be so fine-meshedthat it gets a relatively short lifetime. However, such a spark-arresterscreen can only to a limited extent put out flames.

PURPOSE OF THE INVENTION

A purpose of the present invention is thus to achieve a muffler thatminimizes the risk of flaming at the exhaust outlet.

A second purpose is to achieve a muffler providing an improved coolingof the exhaust gases before these are brought in contact with fresh air.

SUMMARY OF THE INVENTION

These and other purposes of the invention are achieved in a muffler ofthe initially mentioned kind, in which an outlet duct is arranged inconnection to the outside of the housing, said outlet duct comprises afirst section arranged to conduct the exhaust gases in a first directionin parallel with the outside of the housing, and a second sectionarranged to conduct the exhaust gases in a second, opposite direction,whereby said first and second sections have an essentially equally largecross-section area and will forward the exhaust gases up to a mouth. Theinvention is mainly intended for mufflers equipped with a catalyticconverter. However, it is also applicable for engines generatingespecially hot exhaust gases for other reasons.

This outlet duct is not to be mistaken for the type of guide plate forfresh air that is shown in WO9602741. This guide plate is locatedcompletely outside the muffler housing and is adapted to guide the freshair past the exhaust outlet in order to thereby cool down and spread outthe exhaust gases. Even though the exhaust gases by means of the guideplate are forced to change direction by 180 degrees, this change ofdirection will occur first after the exhaust gases have passed throughthe outlet and thus been brought in contact with fresh air.

Instead, according to the subject invention a closed outlet duct fromthe inner outlet of the muffler up to the mouth is created, and first onthe outside of said mouth fresh air from the outside can be brought incontact with the exhaust gases. Fresh air is thereby efficientlyprevented from coming in contact with the over-heated surfaces (“hotspots”) of the catalytic element as well as the surrounding platesurfaces inside the muffler, by so called back-pulsation.

Furthermore, since the exhaust gases are forced to pass through thetwo-way directed labyrinth forming the outlet duct, said exhaust gaseswill be sufficiently cooled to prevent any flames from occurring at themouth of the duct. It is hereby advantageous if the labyrinth is locatedoutside the muffler housing to provide an especially good cooling.

Both opposed directed sections of the outlet duct have an essentiallyequally large cross-section area, i.e. the area of the downstreamsection represents 50–200% of the upstream section and preferably70–150%. Hereby there will not be any larger pressure difference overthe curve that is the result of the change of direction. Thereby asubstantial back-pressure can be maintained right up till when theexhaust gases are leaving the mouth.

A spark-arrester screen can be arranged between the inner outlet of themuffler and the outlet duct for arresting sparks brought by the exhaustgases. The spark-arrester screen can also be arranged in the outlet ductor at the very exhaust outlet. Thereby a combination of spark-arresterand outlet labyrinth is achieved, thus providing a satisfactoryelimination of both sparks and flaming.

The outlet duct is preferably orientated in parallel with the outer wallof the muffler housing. This orientation is advantageous fromconsiderations of space as well as for the functioning of the outletduct. The cooling can be improved in that the outlet duct is located atthe same level as the outside of the muffler. Furthermore, since thefirst section is orientated along the muffler housing a relativelysubstantial change of the flow direction will occur already when theexhaust gases are arriving at the first section. The change of directionbetween the first and the second section will thereby become even moreeffective. For the same reason it is particularly preferable that thesecond section is located outside the first section counted from thehousing, so that the sections are located outside each other.

According to a preferred embodiment the first section is embodied of afirst curved, elongated baffle (duct) having an end-gable located at theinner outlet and an aperture located at a distance from this, and thesecond section is embodied of a second curved baffle having an end-gablelocated at said aperture, and a mouth located along the first baffle,whereby the second section is embodied of a space created in betweensaid first and second baffles. The labyrinth, which is created in thismanner has been found to function satisfactory, and both parts caneasily be mounted tight to the muffler housing. Both baffles can easilybe adapted considering curving and length in order to achieve an optimaloutlet labyrinth.

A bulge can be arranged on the first baffle, i.e. outside said mouth, sothat the exhaust gases released from the mouth will be spread out by thebulge. Owing to the fact that the outflowing exhaust gases are spreadout the still comparatively hot exhaust gases will be prevented fromfollowing a single flow with a high temperature. The outspread exhaustflow will simply be cooled down faster since it will be brought incontact with a greater volume of ambient air.

The outlet duct is according to an especially preferred embodimentpreferably orientated in a crosswise direction of the cylinder of theengine.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will in the followingfor the purpose of exemplifying be described in greater detail withreference to the accompanying drawing figures.

FIG. 1 shows in an exploded view a catalytic muffler equipped with anoutlet duct according to an embodiment of the invention.

FIG. 2 illustrates the parts of the outlet duct according to FIG. 1 inan exploded view from below.

FIG. 3 illustrates the outlet duct according to FIGS. 1 and 2 in anassembled condition.

FIG. 4 shows the outlet duct in a cross-section along the line IV—IVaccording to FIG. 3.

FIG. 5 shows the outlet duct in a cross-section along the line V—Vaccording to FIG. 3.

DESCRIPTION OF PREFERRED EMBODIMENTS

The catalytic muffler shown in FIG. 1 in an exploded view is in itselfof a known type, however equipped with an outlet duct according to anembodiment of the invention. The muffler comprises a housing 1, 2consisting of a housing 1 and a lid 2, preferably made from a thin metalsheet or another material with similar characteristic features. Thehousing 1 is intended to be mounted to an exhaust outlet of an enginecylinder (not shown), and has therefore an inlet 3, while the lid 2 hasan inner outlet 4 for the exhaust gases cleaned by the catalyticconverter. Distance elements 5 a–c are arranged between the housing 1and the lid 2, and are intended to penetrate through for the purposeconfigured apertures 6 a–c in the lid 2 and to support against the rearwall of the housing 1 around apertures 7 a–c.

Between the housing 1 and the lid 2 an intermediate wall 10 is arranged,having an annular area 11 with apertures 12, at which an annularcatalytic converter element 13 is intended to be mounted by means of aring-shaped covering element 14 provided with apertures. Theintermediate wall 10 also has three larger apertures 15 a–c, intended tobe penetrated by the distance elements 5 a–c.

On the outside of the lid 2 an outlet duct in the form of a “labyrinth”17, 18 is located, consisting of two sections directed opposed eachother. In the shown example each section is separated by a curveddivider 17, 18, or baffle made of plate material, which will bedescribed more in detail in the following. Between the lid 2 and thelabyrinth 17, 18 a spark-arrester screen 19, of an in itself known type,is arranged by means of attachment means 20.

The catalytic muffler according to FIG. 1 can be mounted in thefollowing way:

Initially the catalytic element 13 is placed onto the intermediate wall10 and thereafter the covering element 14 is mounted to the wall. Thering-shaped covering element 14, which preferably in similarity with theintermediate wall is made of plate material, can be soldered or weldedonto the intermediate wall 10, with the catalytic element 13 located inbetween. Thereafter the intermediate wall 10 together with the catalyticelement will be placed into the housing, where it will support against astop 21 extending around the housing.

At the lid 2 the parts of the labyrinth 17, 18 will be soldered orspot-welded, so that the outlet duct is created. In the one end of thelabyrinth, preferably that in connection to the inner outlet 4 from thelid, there should be left an opening, into which the spark-arresterscreen 19 can be inserted and attached by means of a screw 20 orsimilar. By this design the spark-arrester screen can easily be replacedif required, or also be dismantled if desired.

The lid with the labyrinth 17, 18 can now be arranged at the housing 1,i.e. above the intermediate wall 10, which thereby will be clampedbetween the housing 1 and the lid 2, and then be fastened in a suitableway, e.g. by welding or soldering. Thereafter the distance elements 5a–c are inserted through apertures 6 a–c in the lid and welded togetherin a position where they stop against inner wall 1 a of the housing 1,said distance elements are preferably made of metal sleeves resistant topressure in a longitudinal direction. The distance elements 5 a–c canthereby be used to attach the muffler onto an engine cylinder (notshown) by means of penetrating attachment means 22 a–c.

In FIG. 2 the curved baffles 17, 18 which are forming the labyrinth ofthe outlet duct, are shown in an inversed view where it becomes moreevident how the duct sections, which in the FIGS. 2–5 are designated byreference numerals 30 and 31, are created. The first baffle 17 iselongated and has one short side that is sealed by end wall 32 and hasan aperture 33 in its other short side. At a location between the bothshort sides of the baffle a bulge 34 is created since the curving ishigher at this location. Furthermore, around the entire baffle a flange35 extends for enabling fastening of the baffle in a simple way onto theoutside of the muffler housing. The other baffle 18 is shorter, and hasa somewhat higher curving, however, in similarity with the first baffleit has an end wall 36 and an aperture 37. Furthermore, it is adapted tobe mounted above the first baffle 17 and has its end wall 36 located atsome distance outside the aperture 33 of the first baffle 17, and hasits aperture 37 located between the bulge 34 and the aperture 33. Thebaffles are in this position mounted as shown in FIGS. 3–5.

The above-mentioned outlet duct's first section 30 is thus delimited bythe muffler lid 2 and the first baffle's curved inside, and the duct'sother section 31 is embodied of a space in between the baffles createdby their respective curving. Owing to the fact that the second baffle'send wall 36 is located at a distance outside the first baffle's aperture33, a curve 38 that connects the two sections 30, 31 is hereby created.The second section 31 ends up in a mouth 39 having an essentiallyU-shaped cross-section. The extension of the outlet duct is most clearlyillustrated in FIG. 4.

Consequently, as illustrated in FIG. 5 the first section 30 has anessentially rectangular cross-section, while the second section 31 hasan essentially U-shaped cross-section. A characteristic feature of thepresent invention is that both sections, in spite of their differentcross-sectional shapes, have an essentially equally largecross-sectional area.

During operation uncleaned exhaust gases are led from the engine'scylinder outlet into the muffler's first chamber, located between thehousing 1 and the intermediate wall 10, and are forced to pass thecatalytic element 13 through the apertures of the covering element 14 aswell as the intermediate wall 10. The in this way cleaned and very hotexhaust gases are thereby led into the second chamber of the muffler,located between the intermediate wall 10 and the lid 2, and then outthrough the outlet 4. Where applicable the exhaust gases pass throughthe spark-arrester screen 19 where possible following sparks can bearrested, thereafter the exhaust gases arrive at the outlet duct 17, 18according to the present invention.

The exhaust gases will now follow the way shown in FIG. 4, in a firstdirection A along the first section 30, through the aperture 33, aroundthe curve 38, and then in the other direction B along the second section31, and finally out through the mouth 39. Outside said mouth the exhaustgases will flow towards the bulge 34, which then will spread them out.

It is evident for the skilled man that the above described embodimentcan be modified in many different ways within the scope of the appendedpatent claims, e.g. the illustrated muffler is only one of a number ofconceivable variants, with different shape and design of the housing, aswells as the location of a possible catalytic element and the flow pathof the exhaust gases.

Furthermore, the outlet duct with its two opposed directed sections 30,31 can be embodied in many different ways. E.g. the sections can belocated side by side instead of outside each other, or can also haveanother shape than the one illustrated here. The outlet duct can also beimmersed, either completely or partly, in relation to the outside of thehousing, e.g. the first section can be created between an immersed partof housing's outside and a covering plate. Alternatively, one or twointernal plates could create the first section 30, and possibly also thesecond section 31 of the outlet duct together with the housing. Thiswould lead to a less effective cooling of the exhaust gases.Furthermore, the muffler could have one or several exhaust outletslocated on one or several sides of the muffler. The exhaust outletscould also be of a mutually different type.

1. A muffler comprising a muffler housing (1, 2) consisting of a housing(1) and a lid (2) or cover (2) having at least one inner outlet (4) forexhaust gases cleaned by a catalytic converter element (13) mounted inthe housing, said muffler has an outlet duct (30, 31) through whichexhaust gases are intended to pass, characterized in that the outletduct (30,31) is arranged downstream of the inner outlet (4) and locatedon the outside of the lid (2) to provide an especially good cooling,said outlet duct comprises a first section (30) arranged to lead exhaustgases in a first direction (A) in parallel with the outside of the lid(2), and a second section (31) arranged to lead exhaust gases in asecond, essentially opposite direction (B), and said second section (31)is located outside said first section (30), counted from the lid (2),and said first and second sections (30,31) have an essentially equallylarge cross-sectional area and will forward the exhaust gases up to amouth (39).
 2. A muffler according to claim 1, whereby the outlet duct(30,31) is orientated in parallel with the outer wall of the mufflerhousing (2).
 3. A muffler according to claim 2, whereby said firstsection (30) is embodied of a first curved, elongated baffle (17) havingan end-gable (32) located at the inner outlet (4) and an aperture (33)located at a distance from the outlet (4) and whereby said secondsection (31) is embodied of a second curved baffle (18) having anend-gable (36) located at said aperture (33), and a mouth (39) locatedalong the first baffle (17), whereby said second section is embodied ofa space (31) created in between said first and second baffles (17,18).4. A muffler according to claim 3, whereby a bulge (34) is created onthe first baffle (17) located outside said mouth (39), so that theexhaust gases released from the mouth (39) will be spread out by thebulge (34).
 5. A muffler according to any one of the preceding claims,whereby the outlet duct (30,31) is orientated in a crosswise directionto the direction of the cylinder of the engine.
 6. A muffler accordingto claim 1, whereby a spark arrester screen (19) is mounted between themuffler's inner outlet (4) and the outlet duct (30,31).